1. Field of the Invention
This invention relates to an injection control apparatus.
More specifically, the invention relates to an apparatus for controlling extruders used to fill a mold or a portion thereof with a predetermined quantity of a thermoplastic material.
2. Description of the Prior Art
There are presently available many such injection control apparatuses, for example, those disclosed by U.S. Pat. Nos. 3,647,309, which issued to R. H. Thompson on Mar. 7, 1972 and 3,865,528 which issued to L. G. Roess on Feb. 11, 1975.
The apparatus of the first mentioned U.S. patent is intended to control moving parts of an injection molding machine using sensing potentiometers having sliding contacts mechanically connected to the moving parts for producing sensing voltages varying linearly with movement of such parts. Reference voltages are compared with the sensing voltages to actuate solenoids or other controls for initiating and terminating various functions of the molding machine.
The Roess patent discloses an electronic interpolator for effecting relative movement between a die head and pintle to provide a variable orifice through which extrudable material is forced to form a parison of controlled wall thickness. The patent contemplates generating a continuously variable signal by an electrical transducer slaved to some movable element of the apparatus. Two or more programs may be serviced by a single electronic interpolator means for simultaneous control of a corresponding number of separate functions.
Even though such apparatus are available, there exists a need for a simple injection control apparatus, which accurately controls the shot size, i.e., the quantity of material dispensed by an extruder into moving molds during each extrusion operation.
The object of the present invention is to provide a relatively simple injection control apparatus for effectively controlling the quantity of material dispensed by an extruder in accordance with the volume of the mold cavity.